Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is geared to a generator for producing electricity.
For example, FIG. 1 illustrates a wind turbine 10. As shown, the wind turbine 10 includes a nacelle 14 that typically houses a generator. The nacelle 14 is mounted on a tower 12 extending from a support surface (not shown). The wind turbine 10 also includes a rotor 16 that includes a plurality of rotor blades 20 attached to a rotating hub 18. As wind impacts the rotor blades 20, the blades 20 transform wind energy into a mechanical rotational torque that rotatably drives a low-speed shaft 22 (FIG. 2). The low-speed shaft 22 is configured to drive a gearbox 24 (FIG. 2) (where present) that subsequently steps up the low rotational speed of the low-speed shaft 22 to drive a high-speed shaft 26 (FIG. 2) at an increased rotational speed.
The shaft 22 or 26 may be rotatably coupled to a generator of an electrical power system. In some embodiments, for example, the generator is a doubly-fed induction generator or DFIG. In other embodiments, the electrical power system is a full conversion system only coupled to the stator of the generator. In either case, the electrical power system provides the power generated by the wind turbine 10 to the power grid as electrical power in a suitable form for use in the power grid.
One issue that needs to be addressed in power systems is harmonics. Power generation systems connected to a utility grid must meet certain agency requirements for harmonics. Accordingly, power systems which include features for reducing the harmonic currents being injected into the power grid, particularly in view of agency harmonics requirements, would be advantageous.